Good gut bacteria start disappearing days after ICU admission

Patients in intensive care units have very different microbiomes than those of healthy patients, and ICU patients' bacterial imbalance worsened during their hospitalization, according to a study recently published in mSphere. This imbalance can leave patients more vulnerable to hospital-acquired infections.

Researchers collected skin, stool and oral samples from 115 ICU patients spread across four hospitals in the United States and Canada. They analyzed the samples' bacterial populations at 48 hours after admission and after 10 days in the ICU or at discharge.

They then compared those results to samples from healthy people who participated in the American Gut project, a crowd-sourced project focused on characterizing the human microbiome.

Comparatively, ICU patients' samples had lower levels of firmicutes and bacteroidetes bacteria and higher levels of proteobacteria, which can include pathogens.

"The results were what we feared them to be," Paul Wischmeyer, MD, the study's lead author. "We saw a massive depletion of normal, health-promoting species."

What struck Dr. Wischmeyer and the team was the speed with which the patients' microbiomes changed. "We saw the rapid rise of organisms clearly associated with disease…In some cases, those organisms became 95 percent of the entire gut flora — all made up of one pathogenic taxa — within days of admission to the ICU," he said.

Tracking the microbiome along with other vital signs could be a useful tool to identify risks before patients become symptomatic, Dr. Wischmeyer said.